This invention relates to a battery charger which charges a battery using solar cells, and to the solar cells used for battery charging.
In recent years all types of electrical equipment have been miniaturized and made lightweight, and many portable electronic products have become available. Since commercial alternating current cannot be used with portable electrical equipment, batteries are used. Single use batteries such as dry-cell batteries and rechargeable batteries such as nickel-cadmium batteries are well known battery power sources. However, since rechargeable batteries can be repeatedly re-used simply by charging and have large capacity allowing high current discharge, they are extremely convenient to use.
It is known that rechargeable batteries can be charged using commercial alternating current or using solar cells. Commercial alternating current has the drawback that it is typically used only indoors and cannot be used outdoors to immediately recharge electrical equipment with low batteries. For this reason, it is necessary to carry a spare battery. A further drawback of charging with commercial alternating current is that rectifying circuitry is required to convert the alternating current to direct current. This makes the charging circuitry more complicated.
On the other hand, rechargeable batteries can be charged by solar cells indoors or outdoors as long as the solar cells produce electricity. Therefore, batteries can be recharged even when they run-down while portable equipment is being carried about. Since solar cells do not use commercial alternating current, they are economical. Further, since solar cell output is direct current, no alternating current conversion circuitry is required.
However, since 100% of the light energy cannot be converted to electrical energy, sufficient output cannot easily be obtained. For this reason, the light receiving area of solar cells must be made large in order to obtain enough output to charge batteries. Since making the solar cell light receiving area large means making the solar cells themselves large, this has the drawback that the larger the solar cells are made, the less portable they become.
Advances in rechargeable battery technology has resulted in commercial products such as high capacity nickel-hydrogen batteries and lithium ion batteries with higher voltage per cell than nickel-cadmium batteries. Consequently, charging current and voltage must be increased for charging these various types of batteries and the light receiving area of the solar cells must be further increased. For this reason, solar cells must be made larger and larger resulting in the drawback that it is difficult to make a battery charger powered by solar cells which is portable.
It is the first object of this invention to present a battery charger with solar cells which is easily portable, which can be quickly set to recharge run-down batteries in portable electrical equipment used outdoors, and has solar cells which have sufficient output for charging batteries.
Often in the case of portable electrical equipment with rechargeable batteries, the equipment is put in a carrying case or bag for transport. Japanese Utility Model Publication No. 61-129436 issued Aug. 13, 1986, discloses a bag which carries rechargeable batteries and which can charge those rechargeable batteries with solar cells. This bag is shown in FIG. 2. The bag of FIG. 2 is a mountain climbing type backpack with solar cells 210 provided on the upper flap portion of the bag. The rechargeable batteries 213 are retained within the bag and the solar cells 210 are connected to the rechargeable batteries 213 through lead wires 26 and the battery charger 214. As a result, the rechargeable batteries 213 are charged by the solar cells 210.
It is generally known that battery temperature rises when rechargeable batteries are charged. It is also known that leaving rechargeable batteries in a high temperature environment for long periods invites battery degradation. However, heat is enclosed within the bag described by the above mentioned application when the upper flap is closed and, furthermore, the batteries generate heat when they are charging.
It is the second object of this invention to provide a bag which can carry portable electrical equipment housing rechargeable batteries without degrading those rechargeable batteries and, further, can charge those rechargeable batteries while the electrical equipment is within the bag.
Incidentally, the footprint of large solar cells can be made smaller when not in use if the solar cells are designed to be folded up. Japanese Non-examined Utility Model Publication No. SHO61 123550, issued 1986, discloses a solar cell apparatus comprising a plurality of solar cell devices connected by leads which can bend. This configuration of solar cell apparatus has the characteristic that it can be folded up and made compact when not in use. Further, solar cells can be mounted on folding parts of electrical equipment such as portable telephones which have a case structure allowing parts to bend and fold up. Apparatus with solar cells mounted on folding parts of the case have solar cells on more than one surface of the case and have the characteristic that solar cell area and hence power output can be made larger.
The solar cell apparatus disclosure mentioned above has the structure shown in FIG. 1. The folding solar cell apparatus has flexible leads connecting solar cell devices. The flexible leads are reinforced by a protective cover that coats both sides of the leads making them difficult to damage. The surfaces of the solar cell devices are also coated with a protective cover.
The solar cell apparatus shown in FIG. 1 has the characteristic that since the leads 2 are flexible and can be used as hinges, the apparatus can be conveniently used in various applications. However, connection of the leads 2 is extremely labor intensive, and this structure has the drawback that efficient lead connection for inexpensive mass production is difficult. This is because both sides of the leads 2 are coated with a protective cover 4 after connection to solar cell device 1 terminals; then the surfaces of the solar cell devices are coated with a protective cover 5. Manufacturability is even worse if already complete solar cell devices 1 coated with a protective cover 5 are used and the devices are connected with leads 2. This is because the protective cover 5 on the solar cell devices 1 must be removed over the terminals, leads 2 must be connected to the terminals, and a protective cover 4 must be applied over both sides of the leads 2 and over the surface of the terminals. Processing difficulty is reflected in the manufacturing cost of the solar cell apparatus and limits its application.
The solar cell apparatus shown in FIG. 1 has the further drawback that the leads 2 are easily broken at their interface with each solar cell device 1. When adjacent solar cell devices 1 are folded up, the leads 2 bend with a small radius of curvature at their interface with each solar cell device 1. The leads 2 are coated with a flexible protective cover 4, but the solar cell devices 1 are coated with a stiff protective cover 5. At an interface with a solar cell device 1, the leads 2 have a discontinuous section which transitions from a deformable region to a non-deformable region and bending in this region easily damages the leads 2. The fact that the leads 2 are easily broken not only limits their application but also makes malfunctions due to open circuited leads common. Applications are limited because the apparatus cannot be used where the leads are repeatedly bent and flexed.
A further drawback of this apparatus is the difficulty in determining open circuits in the leads 2. This is because even though a lead 2 may be open circuited, the protective cover 4 on both sides of the lead 2 may not be broken. External visual inspection of a broken lead 2 may therefore show it to be connected. Further, since the leads 2 are flexible and free to deform elastically, a broken section of lead 2 as well as an unbroken section of lead 2 are both free to deform. For this reason it may be difficult to determine a lead 2 open circuit at the degree to which the lead 2 can deform. This a further cause of difficulty in determining open circuits in the leads 2.
It is the third object of this invention to present a flexible solar cell apparatus that can be manufactured efficiently and inexpensively in quantity. It is a further primary object of this invention to present a flexible solar cell apparatus in which open circuited leads are not only prevented but also are easy to determine in the unlikely event that they occur.
In a folding solar cell apparatus with flexible leads, lead bending is limited to a minimum radius of curvature. This is because lead bending with an extremely small radius of curvature results in failure to restore the original lead shape. In a folding solar cell apparatus with a plurality of solar cell devices connected with the ability to bend at their boundaries, it is desirable to allow folding with as small as possible a radius of curvature at the boundaries. This is because bending with a large radius of curvature does not allow the apparatus to fold into a thin shape. In particular, a solar cell apparatus with many interconnected solar cell devices which cannot be folded with a small radius of curvature at the leads has the drawback that it will be quite thick when folded.
It is thus another further object of this invention to present a solar cell apparatus in which the leads can bend with a small radius of curvature resulting in a thin folded shape, and while the leads are frequently bent, lead damage and poor connection can be markedly reduced.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.